Wiring up 110/220VAC to 6V center tap transformer

Question

I have a center tap transformer that does 110 or 220VAC stepdown to two 6V rails (with opposing phases). On the 110/220 side there are what appear to be two separate rails, and the wiring diagram is a bit confusing to me:

In order to use this on a 110VAC source and get the proper 6VAC output, how do I wire up the mains side? Per the diagram it seems like I would wire the mains to a single black/red set (with the other set tied off and insulated), or possibly tie them in parallel (black to black, red to red). Is the idea that for 220VAC input I'd tie the center black and red together and wire the 220 mains to the outer pair of wires?

Answer 1

Your understanding is correct.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Primary and secondary windings.

Note that the voltage between the two blue terminals will be 12 V AC.

You could use only one primary for 110 V operation but the maximum power you can draw from the transformer would be halved.

Answer 2

Parallel black to black. Parallel red to red. Apply 110 Vac between black and red. Take out 6 Vac between blue and yellow.

Yes, the idea for 230 V operation is to tie them in series. Very common arrangement to be able to have the same transformer for the world market. Dual 6 V secondaries is most probably to be able to get symmetrical + and - voltage DC around center ground on the secondary.